Devices for adjustably clamping two elongated elements with respect to one another are well known in the prior art. Such compound clamps are employed extensively in the construction industry, for example, to effect the proper positioning of a construction stringline. A stringline, which serves as a guide for an automatic machine control employed in construction work, must be properly disposed both horizontally and vertically so that the machine under control will be accurately guided.
In the main, such a stringline is supported on a stringline rod, which is generally horizontally disposed and is formed with a stringline engaging groove. The line rod is clamped to a vertically disposed stake by an adjustable clamp. The clamp adjustment mechanisms employed in the prior art are generally mechanical in nature, and as such often required the use of wrenches or screwdrivers to effect the necessary adjustment. This has often resulted in bent adjustment screws or stripped threads which may permanently damage the clamp bracket.
Additionally, the use of auxiliary tools, such as screwdrivers and socket wrenches to adjust these clamps, is time consuming and therefore increases construction costs.
Moreover, many of the prior art stringline clamps do not provide independent horizontal and vertical adjustments of the stringline. Unless such adjustments are independently provided, an excessive number of repeated readjustments are required until final stringline grade is achieved.
Prior art clamps for engaging one or more elongated elements are shown in U.S. Pat. Nos. 2,123,425; 2,968,850; 3,045,499 and 3,233,297.